The present invention relates to a dental articulator and a conversion plate therefor which are used by dentists and dental technicians in the clinical field during treatment of the occlusion of upper and lower dentition and during the creation of prosthetics for reproducing and analyzing physiological occlusion states relating to the intercuspal position and the posterior occlusal position, wherein using an occlusal plane table with a forward inclination of 10 degrees, an upper jaw dentition plaster model is mounted onto an upper jaw frame and in parallel with the Camper plane which is a prosthetic plane, a lower dentition plaster model is mounted onto a conversion plate which has been mounted and fixed to a lower jaw frame serving as a base, and the physiological relationship of upper and lower jaws is reproduced so that the upper and lower jaws are brought into the state of centric relation (anterior superior position), and further physiological occlusion states relating to the intercuspal position and to the posterior occlusal position can be reproduced or analyzed by the operation of shifting said conversion plate and adjusting all directions of lower jaw movement.
The physiological occlusion states herein means the intercuspal positionxe2x80x94the starting point and stopping point of occlusion, and the posterior occlusal positionxe2x80x94the limited position where ligament is tensioned.
In some cases, this conversion plate, if used as an accessory part to be incorporated into an existing articulator which has in advance been disassembled for re-assembly, can be provided as an accessory part for converting the function of said articulator into that of this new articulator for reproducing jaw movement in a person more accurately.
Since it is effective to reproduce the intercuspal position and the posterior occlusal position in the field of prosthetic treatment, there have been proposals on simulating these positions in an articulator and other treatment tools. For the prosthetic treatment of partial or full dentures, such instruments are known as an ear-face-bow for reproducing the positional relationship between the upper jaw and the skull, an occlusal plane table for arranging denture detention, a Broadrik""s occlusal plane analysis table for arranging the lower jaw occlusal cusp on an arc of 10 cm radius, and Gerber""s articulator for reproducing the posterior occlusal position.
For example, the ear face bow is widely employed with the intention of reproducing the Frankfurt plane (FH plane) using the orbitale (Or) and the opening of external auditory meatus (Po). There still remains a problem, however, regarding the precision in the horizontal direction since a rod is inserted into the external auditory meatus of feeble. tissue.
On the other hand, in case of full dentures, the occlusal plane determination method using the Camper plane is highly precise in the horizontal direction and has an advantage that the median line can be determined using an upper jaw occlusion model. In the conventional technique of this method, however, a problem still remains regarding the Balkwill angle on the sagittal plane (sagittal upward direction) since the upper Jaw frame and the occlusal plane table are set to be parallel with each other.
Further, in the Broadrik occlusal plane analysis table for arranging the occlusal cusps of the lower jaw on an arc, there remains a problem that the right and left Spee curves do not match with each other since each Spee center is established separately.
Further, Gerber""s articulator, which can reproduce the posterior occlusal position, has a problem in the amount and direction of posterior movement.
That is, in well-known Gerber""s articualtor (trade mark: Condylator ), a slide clutch is attached to the area of temporomandibular joint so that the intercuspal position and the posterior occlusal position can be reproduced respectively when the clutch is locked and unlocked. FIG. 15 shows a photograph carried in a catalogue. This type of articulator has not yet widely been used in Japan because of its high cost.
It has been advocated that the jaw oral cavity system in a person not merely conduct the movements relating to the mastication function but also has a function of helping the head balance in the directions of forward, backward, left, and right, that is, for the inertia balance system to determine position and axis of the head in posture control (hereafter referred to as a new guiding principle).
Thus, the occlusion dentition is determined by the activity of the jaw closing muscles with the temporomandibular joint as a fulcrum. In a normal case, the muscle activity during tapping at the intercuspal position maintains balance in the directions of left, right, front, and back, and that stabilized position is anatomically called the stabilized condyle position and is clinically called the centric relation (anterior superior position).
Techniques in the prior art, however, only focus on one element of the mastication function and lack an overall viewpoint. Further, they reveal inconsistency in that different methods are employed for handling jaws with teeth and those without teeth.
Accordingly, a method based on the new guiding principle for diagnosing and treating physiological occlusion becomes important to clinical workers treating patients with temporomandibular arthrosis and creating prosthetics that protect susceptible retrodiscal tissue of the temporomandibular joint.
The inventor has been making some proposals on methods for diagnosing and treating physiological occlusion. Briefly speaking, at the physiological occlusion state, the lower jaw normally has a movement range of about 12 mm for forward and about 1.2 mm xc2x11.0 mm for backward from the intercuspal position with the teeth closed at the centric relation (anterior superior position). In the forward movement, the incisor area describes a movement curve in a forward and downward direction due to guiding contact between the upper incisors lingual side and the lower incisors labial side, and the condyle area describes a movement curve in a forward and downward direction on a downwardly, convex arc. In the posterior movement, the molar area describes a movement curve in a backward and downward direction due to the guiding contact between the mesial slopes of the lingual cusps of the upper molars and the distal slopes of the buccal cusps of the lower molars, and the condyle area describes a movement curve in a backward and upward direction on an upwardly convex arc [(For example, Fujita Kazuya: Temporomandibular Arthrosisxe2x80x94Criteria on Physiological Occlusion (Dental Booklet Series 35, (Dental Forum, 1997)].
Though a Gerber""s Condylator intends to reproduce the intercuspal position and the posterior occlusal position using a clutch at the area of temporomandibular joint, the instrument is unsatisfactory because it fails in representing the accurate behavior of temporomandibular joint. Namely, though it is primarily known that condyle movement is about 0.2 mm to 2.0 mm in its amount and is backward and upward about 20 to 30 degrees with respect to the Frankfurt plane in its direction, Gerber""s Condylator moves only in the backward and downward direction and the movement amount is about 0.5 mm.
An articulator commonly used by dentists and dental technicians in Japan (hereafter referred to as a conventional articulator) is not structured to allow the temporomandibular joint area to move backward, that is, since the conventional articulator does not make it possible to reproduce the posterior occlusal position while making it possible to reproduce the intercuspal slope. In addition, the function (clutch) of Gerber""s Condylator can hardly be incorporated to use. FIG. 14 shows an example of a conventional articulator. The reference numerals in this drawing do not correspond to those in other attached drawings for the present invention.
In these situations, it is highly expected to develop a new dental articulator based on a new guidelinexe2x80x94possessing a bilateral symmetry under the physiological gravity, allowing an occlusal plane to be set to a forward incline of 10 degrees, possessing a Spee curve in harmony with the lower jaw pendular movement in a person, allowing the intercuspal or posterior occlusal position and the balanced cusp slopes toward left, right, front, and back to be reproduced.
One approach in this case would be to improve the conventional articulator having the existing function of Gerber""s articulator Condylator (if detailed, an improved function for reproducing jaw movement), that is, adding a part (a converter plate of the present invention) as a new structural element for converting the conventional function into that of a new articulator while taking advantage of the existing articulator""s structure. Then, the goal will effectively be achieved by combining various technologies in the prior art (collecting the functions from conventional instruments).
The present invention has been developed in light of these circumstances and intends to resolve the above issues and to provide an embodiment of a new dental articulator based on a new guiding principle. Another object of the invention is to provide a conversion plate for a dental articulator so that jaw movement in a person can be reproduced more accurately by simply operating said plate.
In some cases, this conversion plate is provided as a single part because the plate, if used as a part to be incorporated into a conventional articulator which has in advance been disassembled for re-assembly, can convert the function of said articulator into that of this new articulator.
A first aspect of the invention is a dental articulator which actualizes the load receiving function and the tractive function to be operable in all the directions which are equivalent to those in the function of a temporomandibular joint in a person, comprising:
an occlusal plane table formed to have a slant surface with a forward inclination similar to that of an occlusal plane in a person;
an occlusion analysis plate with averaged positions established and drawn at multiple locations for a Spee center and a posterior movement axis which are constitutional elements in a person;
an incisor guiding plate provided with an inverted slant conical surface to map the forward, backward, left, and right intercuspal inclinations for reproducing jaw movements in a person toward forward, backward, left, and right so that the tip of an incisor guiding pin is slid along said slant surface; and
a conversion plate mounted to a base of a lower jaw frame together with a lower jaw plaster dentition model for operating and reproducing physiological states for the intercuspal position and the posterior occlusal position in a person.
Thus, the articulator makes it possible to reproduce or analyze the physiological occlusal states.
The articulator herein is preferably provided with a face bow as an accessory part for recording the Camper plane which is parallel to an occlusal plane in a person.
A second aspect of the invention is a conversion plate for a dental articulator which, including a lower jaw frame as a base, is mounted (incorporated) together with a dentition plaster model onto (into) said dental articulator whose condyle path angle has been set to 30 degrees so that physiological occlusion states related to intercuspal position and posterior occlusal position are operated and reproduced by the shift operation, wherein a main body of said conversion plate is divided into an upper structural member and a lower structural member; binding surfaces of both members are formed to rise and fall so that the surfaces can be fitted or engaged with each other by male and female elements and can slide in the direction parallel with the Condyle path angle; both said members are provided on the left and right side faces thereof with either a threaded hole or an oblong hole for a temporary fixing by a screw; and said upper structural member with said lower jaw dentition plaster model mounted is slid on said binding surfaces.
Here, said male and female elements are a recess and a protuberance, and triangular elements, said binding surfaces fit with each other by means of the recess and projection and engage with each other by the triangular elements, and said binding surface related to said engagement is formed to include the two sides crossing at the right in a right triangle with two interior angles of 30 degrees and 60 degrees other than a right angle so that the inclination in said sliding direction and the condyle path angle are the same. Accordingly, both members have such a binding relationship in which both members can slide (be operated to shift) relatively to each other in a forward and downward direction (backward and upward) of 30 degrees in the mounted elevation view.
Thus an occlusal state is relatively converted between said conversion plate and an upper jaw dentition plaster model mounted onto an upper jaw frame of said dental articulator.
That is, {circumflex over (1)} not only the occlusal state related to intercuspal position can be operated and reproduced by engaging and fixing the upper structural member and the lower structural member with each other, {circumflex over (2)} but also the physiological occlusal states related to intercuspal position and posterior occlusal position can be operated and reproduced by sliding the upper structural member and thereafter sliding the lower structural member in a forward and downward direction of 30 degrees and then fixing both members to each other. (The operation procedure is later described.)